As the world population continues to show explosive growth, arable land is rapidly decreasing due to environmental pollution, global warming, and desertification, and chronic food shortage persists mainly in developing countries. Furthermore, the present grain production growth rate of 1.0% is low compared to the annual global population growth rate of 1.4%; furthermore, in the year 2025, when the world population is predicted to exceed eight billion, grain requirements will increase by 50%, further accelerating food shortage. In order to break this serious situation, not only political and economic measures, but also scientific grain breeding strategies that will increase the amount of grain production are necessary. This serious condition can no longer be avoided by conventional breeding, using cross-fertilization and selection techniques alone, and studies on grain plant type aimed at increasing yield, as well as specific and efficient grain breeding are necessary.
When concern was raised on world food crisis in the 1960's, short-culm high-yielding rice called miracle rice was cultivated at the International Rice Research Institute (Philippines), and short-culm high-yielding wheat was cultivated at the International Maize and Wheat Improvement Center (Mexico). World food crisis was avoided due to the rapid spread of both of these varieties. This is the so-called “Green Revolution”. Both varieties showed twice the yield of conventional varieties, and this high-yielding character was caused by a short-culm plant type called a semi-dwarf. However, while application of nitrogenous fertilizers is necessary when aiming for a high yield, this simultaneously induces elongation of the plant, and lodging of the elongated grain by rain and wind dramatically decreases yield. On the other hand, even when fertilizers are applied, short-culm varieties allow an increased yield without succulent growth. That is, both short-culm varieties that contributed to the “Green Revolution” dramatically increased the yield by acquiring lodging resistance. At present, semi-dwarfism of grains greatly contributes to increased yield, but since many grain varieties already utilize semi-dwarf genes, further increase in yield using this technique cannot be expected, and development of grain production technologies that utilize new techniques is necessary.
Rice is utilized as food by 50% of the world's human population. In particular, for those living in Asia, its cultivation characteristics match the highly humid monsoon climate, and not only has it been the source of energy for a long time as the staple diet, but it has also been well established in life and culture. Accordingly, breeding has been carried out in many places, and it has been improved to have characteristics that are convenient for use by humankind. Furthermore, with the recent determination of the genomic nucleotide sequence of rice, tools for molecular genetics are being put into place, and development of new breeding technology using genomic genetics is expected.
To date, various attempts have been made to increase the yield of grains (plants); however, there are no reports of isolation and identification of genes relating to the increase and decrease of the number of flowers and seeds (glumous flowers) that are directly responsible for increase in yield. In addition to the conventional semi-dwarfing of grains, if techniques to regulate the increase and decrease in the number of flowers and seeds (glumous flowers) are developed, further increase in grain yield can be expected.